1. Field of the Invention
The present invention relates to a protective film and a magnetic recording medium having the protective film.
2. Background of the Related Art
A hard coating made of various materials is used as a coating on a sliding resistance member or an antifriction member. A diamond-like carbon (DLC) film made from carbon has been known as such a hard coating. The DLC film is suitable as a surface coating due to its excellent surface smoothness and high hardness. Conventionally, DLC films are formed by a sputtering method, plasma CVD method, and the like.
A magnetic recording medium generally includes a protective film composed of a DLC film on a magnetic recording layer, the DLC film being formed by a plasma CVD method. The protective film is formed for the purpose of protecting the magnetic recording layer from corrosion and being damaged by a magnetic head that comes into contact with or slides on the magnetic recording layer. The magnetic recording medium is, therefore, provided with durable and corrosion-resistant functions.
In recent years, the recording method for a magnetic recording medium has been changing from the longitudinal recording method to the perpendicular recording method capable of increasing the recording density. As with the longitudinal recording method, the perpendicular recording method needs to maintain good electromagnetic conversion characteristics to further increase the recording density by making the protective film of a magnetic recording medium as thin as possible.
Japanese Patent Application Publication No. 2010-55680 (Patent Document 1) proposes a method for processing a protective film, which is formed by a plasma CVD method using hydrocarbon gas, with argon plasma and nitrogen plasma in order to make the protective film thin.
Japanese Patent Application Publication No. H8-129747 (Patent Document 2) proposes the use of a laminated constitution of a DLC film/fluorine-containing DLC film as a protective film of a magnetic recording medium.
Moreover, Japanese Patent Application Publication No. H6-301969 (Patent Document 3) proposes a step of plasma post-processing a protective film made from a carbon-based material, by using inactive gas such as N2 or fluorinated carbon based gas such as CF4. This processing changes the density or resistance of the protective film in a film thickness direction and increases the resistance and density of a surface layer, to reduce the film thickness of the protective film.
Unfortunately, it is difficult for these conventional technologies to simultaneously accomplish reduction in the film thickness of a protective film, improvement of the durability and corrosion resistance of the protective film, and improvement of the bonding strength of the surface of the protective film to a lubricating film.
An object of the present invention is to provide a protective film that is reduced in film thickness and provided with improved durability and corrosion resistance and improved bonding strength of the surface of the protective film to a lubricating film, and a magnetic recording medium having such a protective film. Another object of the present invention is to provide a magnetic recording medium that has the protective film and excellent electro-magnetic conversion characteristics.